The present invention relates to a secondary target device which generates secondary X-rays called fluorescent X-rays by irradiating X-rays (primary X-rays) generated from an X-ray source, and a fluorescent X-ray analyzing apparatus in which the fluorescent X-rays generated from the secondary target device are irradiated to a sample, and fluorescent X-rays generated from the sample are used to carry out a qualitative and quantitative analysis.
In a fluorescent X-ray analysis, a wavelength and an intensity of characteristic X-rays generated from a sample by a irradiating X-rays to the sample are measured, to thereby carry out a qualitative and quantitative analysis of elements in the sample. In the fluorescent X-ray analysis, there have been known a direct irradiation method in which X-rays (primary X-rays) generated from an X-ray source are directly irradiated to a sample, and a secondary target method which uses a secondary target.
In the direct irradiation method, primary X-rays generated from an X-ray tube are directly irradiated to the sample, and fluorescent X-rays generated from the sample are detected by an X-ray detector, such as a semiconductor detector. In the direct irradiation method, since it is possible to analyze a wide range of elements, the direct irradiation method is suitable for a detection of unknown micro-elements.
On the other hand, the secondary target method improves a limit of detecting micro-elements by making excited X-rays monochromatic, and in the secondary target method, primary X-rays are irradiated to the secondary target formed of a material which differs from an anode target of an X-ray tube, to thereby generate fluorescent X-rays including characteristic X-rays which are inherent to the secondary target, so that continuous X-rays included in the primary X-rays are decreased. Therefore, a signal-to-noise (S/N) ratio of the fluorescent X-rays from the sample is improved, to thereby improve the limit of detecting the micro-elements.
In the fluorescent X-ray analyzing apparatus, it has been desired to have a wide applicability for both detection of an unknown micro-element and highly sensitive analysis of a specific micro-element, and there has been proposed an analyzing apparatus which can perform both analyses by the direct irradiation method and by the secondary target method by switching these methods.
Conventionally, as a structure for switching the analysis by the direct irradiation method and the analysis by the secondary target method, there has been used a secondary target device and a fluorescent X-ray analyzing apparatus, wherein a secondary target is disposed at a position diverting from a straight line connecting between an X-ray source and a sample in the secondary target device so as not to directly irradiate primary X-rays from an X-ray tube to the sample, so that only secondary X-rays from the secondary target are irradiated to the sample, and in case the primary X-rays are directly irradiated to the sample, an orientation of the X-ray source is changed.
In the secondary target device and the fluorescent X-ray device described above, although the direct irradiation method and the secondary target method are achieved by one apparatus, there have been the following problems. Namely, since a moving mechanism for rotating the X-ray source is necessary, the apparatus becomes a large size. Also, since an X-ray irradiating condition (irradiation angle and irradiation position) by the direct irradiation method does not always coincide with an X-ray irradiating condition by the secondary target method, there is a problem in an accuracy of a correspondence between the measured data by both methods.
Also, there has been proposed a secondary target device and a fluorescent X-ray device as disclosed in Japanese Patent Publication (KOKAI) No. 10-325814, in which a secondary target is disposed on a straight line connecting between an X-ray source and a sample. In a case of using the secondary target and a case of directly irradiating primary X-rays, irradiated X-rays are switched while an orientation of the X-ray source is fixed.
In the conventional secondary target device and the fluorescent X-ray analyzing apparatus, as described above, there are problems, such as an increase of the size of the apparatus, and an accuracy problem in the correspondence between the measured data due to the difference between the X-ray irradiating conditions with respect to the sample.
Also, in the proposed apparatus described above, since the irradiated X-rays can be switched while the orientation of the X-ray source is fixed, a hollow section of the secondary target is formed into a tapered form in which an opening section at an X-ray source side is large and an opening section at a sample side is narrowed. Therefore, primary X-rays from the X-ray source can be irradiated with a large effective solid angle to the secondary target, but an effective solid angle of the secondary target observed from the sample is reduced, and an angle of observing the sample from the secondary target is shallow, so that enough secondary X-rays can not be irradiated to the sample, resulting in difficulty in obtaining a high measurement sensitivity.
Also, in both conventional apparatus and proposed apparatus, since the secondary X-rays expand on a surface of the sample in a relatively large range, it is difficult to limit an irradiation area on the surface of the sample by the secondary X-rays into a very small area, so that these apparatuses can not be applied to an analysis of a minute portion.
Accordingly, the present invention has been made to solve the aforementioned problems, and an object of the invention is to provide a secondary target device in which X-ray irradiating conditions in switching the irradiated X-rays are held constant, to thereby irradiate enough secondary X-rays with respect to a sample and to irradiate the secondary X-rays to a minute portion of the sample.
Another object of the invention is to provide a fluorescent X-ray analyzing apparatus, in which X-ray irradiating conditions in switching the irradiated X-rays are held constant and enough secondary X-rays are retained to thereby improve a detection sensitivity, and to improve a sensitivity of analyzing the minute portion of the sample.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned objects, in the present invention, an X-ray irradiating condition in case of switching irradiated X-rays is maintained to be constant by disposing an X-ray source, a target main body, and a sample on a straight line, and further, in the structure described above, an effective solid angle of observing a target surface from the X-ray source and an effective solid angle of observing the target surface from a sample irradiation position are substantially enlarged, so that enough secondary X-rays are irradiated to the sample. Accordingly, a high detection sensitivity can be obtained in a fluorescent X-ray analyzing apparatus.
Also, in substantially enlarging the effective solid angles, the secondary X-rays irradiated from a plurality of target surfaces are condensed to an irradiation area of the sample, and an irradiation of the secondary X-rays to an area other than the irradiation area is limited, so that the secondary X-rays are irradiated to a minute portion of the sample. Accordingly, a sensitivity of analyzing the minute portion is increased in the fluorescent X-ray analyzing apparatus. Incidentally, the effective solid angle is a solid angle of observing a predetermined region or surface from a certain point, and in the secondary target device and the fluorescent X-ray analyzing apparatus of the invention, the effective solid angle is formed by treating the target surface as the predetermined region surface.
Therefore, in the target device of the invention, the X-ray source, a sample irradiation position, the target main body having a plurality of target members, and an X-ray blocking member for blocking an irradiation of primary X-rays to the sample irradiation position are arranged on a straight line.
In the target main body, the straight line connecting the X-ray source and the sample irradiation position constitutes a central axis, and the plurality of target members is arranged at positions having different distances from the central axis. In each of the target members, a secondary target material is provided on at least a surface of the target member opposed to the central axis, and the surface described above constitutes a target surface. Incidentally, the secondary target material can be provided on a rear surface of the target member which is not opposed to the central axis, or the entire target member can be formed of the secondary target material, or the target member can be a structure in which the secondary target material is provided on a front surface of an X-ray shielding material as a base or substrate.
The target members can be structured in cylindrical forms, in which a plurality of the target members is disposed on respective circumferences of concentric circles having the straight line connecting the X-ray source and the sample irradiation position as the central axis. Also, as long as the target members have different distances from the central axis, the target members are not limited to the cylindrical shapes, and may be polygonal shapes, or the target members may have a structure in which the target members are disposed only in predetermined diametral directions from the central axis. Also, the target members may be disposed continuously, or separated or dispersed.
In setting the straight line connecting the X-ray source and the sample irradiation position as the central axis, a plurality of the target members is disposed around the diametral direction of the central axis. In case of switching the irradiated X-rays, an X-ray irradiating condition by a direct irradiation method and an X-ray irradiating condition by a secondary target method can be made the same. Incidentally, a disposition of plural target members on the respective circumferences of the concentric circles is an example of the disposition of plural target members around the diametral direction of the central axis.
In this structure, there is formed an effective solid angle of observing the target surface of the target member from the X-ray source or the sample irradiation position. Incidentally, in case the target members are respectively disposed in a direction of a normal line from the central axis to be space away from each other with a predetermined interval therebetween, the effective solid angle constitutes an angle of observing a surface, which is formed in a range of a predetermined distance from a center and extends in a form of a concentric circle, from a certain point. However, in the present invention, the shape is not limited to the concentric circle, and may be selected according to the shapes of the target members and the target surfaces, or the disposition location thereof.
In the secondary target device of the invention, in order to effectively irradiate the secondary X-rays to the sample while the irradiation of the primary X-rays to the sample is being prevented, the primary X-rays from the X-ray source are required not to pass through a space, between the target members and irradiated only to the target surfaces of the target members. Also, the secondary X-rays from the target surfaces are required to pass through the space between the target members and reach the sample irradiation position.
In order to fulfill the above requirements, in the structures of the target main body of the invention, a length of each target member in the central axis direction and a disposition interval in the diametral direction between the adjacent target members are required to satisfy the first condition regarding the primary X-rays and the second condition regarding the secondary X-rays. Here, the first condition constitutes a condition in which an effective solid angle of observing the target surface from the primary X-ray source coincides with an effective solid angle of observing the space between the adjacent target members in the target surface side, and the second condition constitutes a condition in which an effective solid angle of observing the target surface from the sample irradiation position coincides with an effective solid angle of observing the space between the adjacent target members from the sample irradiation position in the target surface side.
Since the target members have the structures as described above, the primary X-rays can be irradiated to the target surfaces without being blocked by the adjacent target members, and the secondary X-rays generated at the target surfaces can reach the sample irradiation position without being blocked by the adjacent target members, to thereby form the effective solid angles of the respective target members. Also, by arranging a plurality of the target members as described above, the respective effective solid angles can be consolidated to have a large effective solid angle which is enlarged as a whole.
Also, in the present invention, the X-ray blocking member is disposed on the central axis. The X-ray blocking member is provided for preventing the primary X-rays generated from the X-ray source from being irradiated to the sample irradiation position, and the X-ray blocking member assures the irradiation of the secondary X-rays to the sample irradiation position.
Further, the fluorescent X-ray analyzing apparatus of the invention constitutes a fluorescent X-ray analyzing apparatus with the target device of the invention, and the fluorescent X-ray analyzing apparatus of the invention is formed of an X-ray source for generating X-rays, a secondary target device of the invention, and an X-ray detector for detecting fluorescent X-rays generated from a sample.
In the fluorescent X-ray analyzing apparatus of the invention, by using the target device of the invention, the X-ray irradiating condition in case of switching the irradiated X-rays can be maintained to be constant, and at the same time, a detecting sensitivity can be improved by obtaining enough secondary X-rays irradiated to the sample.
Also, according to the target device of the invention, by condensing the secondary X-rays with respect to the sample position, the sensitivity of analyzing the minute portion can be increased.
In analyzing the minute portion, it is structured that a shielding member having an opening section, which limits an area of irradiating the secondary X-rays in the sample, on the central axis is provided between the secondary target device and the sample irradiation position. Thus, an irradiation of the secondary X-rays to areas other than the area, to which the secondary X-rays are irradiated, is limited to condense the secondary X-rays to the sample position, to thereby increase the sensitivity of analyzing the minute portion.
Also, one or both of a collimator for directly irradiating the primary X-rays to the sample and a filter for absorbing a part of the primary X-rays are provided, and there is to disposed a driving device for disposing one of the secondary target device, the collimator and the filter on the central axis. The collimator, the filter, or the secondary device is switchably disposed on the straight line connecting between the X-ray source and the sample by the driving device. Accordingly, in case the collimator is disposed, the primary X-rays can be directly at irradiated to the sample, and in case the filter is disposed, X-rays with specific wavelengths in the primary X-rays can be irradiated. Also, in case the secondary target device is disposed, by generating fluorescent X-rays including characteristic X-rays inherent to the secondary targets, continuous X-rays contained in the primary X-rays can be decreased, and a signal-to-noise (S/N) ratio of the fluorescent X-rays from the sample can be improved, to thereby carry out the highly sensitive detection of the micro-elements.